Driving home this past weekend I came to a light, applied the brakes and suddenly my brake pedal went limp, falling through to the floor about 3 inches then caught, seemed like I lost vacuum boost pressure to the brake system. The brakes do work but it feels like a manual system to me, making me put more pressure to the brake pedal and the brakes not being as responsive. There are two vacuum lines coming from the vacuum boost on the firewall, one is capped off the other to the engine, both rubber lines seem good. Did the vacuum boost fail? This is one component I've never replaced since I bought the car 4 years ago. I've never changed one of these before, how difficult is it? Do I have to empty the brake reservior or can I unbolt it, move it out of the way and not have to bleed the brakes? What are the steps to the removal and installation of the vacuum boost? Any insight/tips would be helpful. What is a good replacement part? Engine is a 440/6 pack, the engine/carbs work fine no noticable difference as vacuum opens the outboard carbs. Thanks.

first check the condition of the lines, if good then try a vacuum gauge and see if the booster holds pressure if not have it replaced . it easy just unbolt from peddle and firewall and unbolt master and pull out of the ay (check for seal leakage from the master if there is r/r) also make sure the check valve is good.

I've been experiencing some issues with mine, and from what I gathered if the booster is failing or has failed it would result in a hard pedal and diminished stopping power from a driver standpoint. What you're describing almost sounds as if you may have a small leak. Have you checked for a leak? With the pedal dropping further than normal, I would look there. It could be you need to adjust the rear brakes, if they are out of adjustment that can cause the pedal to drop more than normal. Just a couple of thoughts for you to consider.

Edit: Something for you to try, pump the brakes 3 or 4 times with the car not running, while holding the pedal down start the car, does the pedal drop some and seem to get easier push?

here's a fast check also put your foot on the brake peddle and push then start the car, if the peddle sucks down then more than likely it still works.